Composite fluid machine

ABSTRACT

A composite fluid machine has a first and a second fluid delivering mechanisms. The first fluid delivering mechanism includes an accommodation chamber, a movable body, and a suction space. The movable body is accommodated in the accommodation chamber.. The suction space is defined by the accommodation chamber and the movable body. The suction space is connected to the inlet, and the flow rate of the fluid introduced into the suction space is displaced. The movable body performs a suction movement and a discharge movement.. The second fluid delivering mechanism is combined with the first fluid delivering mechanism and is located upstream of the first fluid delivering mechanism to deliver the fluid to the suction space of the first fluid delivering mechanism.. Lobes of helical roots rotors are twisted in a respective direction around the rotational axis.

BACKGROUND OF THE INVENTION

The present invention relates to a composite fluid machine which has a first and a second fluid delivering mechanisms, and more specifically to a composite fluid machine in which suction flow rate of a first fluid delivering mechanism is displaced while a second fluid delivering mechanism includes helical roots rotors.

Japanese Unexamined Patent Application Publication No. 8-144977, whose corresponding U.S. Patent is also published as U.S. Pat. No. 5,549,463, discloses a dry vacuum pump including a pair of screw rotors in a housing. The pair of screw rotors is rotated while engaging with each other. The fluid is introduced from an inlet into a suction space formed in the housing so as to communicate with the inlet, and is discharged from the housing. Japanese Unexamined Patent Application Publication No. 2006-083783 discloses a screw type fluid machine in which the fluid is introduced into a housing, then compressed, and delivered from the suction side to the discharge side. In such screw type fluid machines, the flow rate of the suction fluid into the suction space is displaced, that is, the increased volume introduced into the suction space per unit time is displaced,. Similarly, the flow rate of the suction fluid is displaced in a scroll type compressor. Such a fluid machine as a screw type fluid machine, a scroll type fluid machine, or a piston type fluid machine and the like is called as a positive displacement fluid machine. When a positive displacement fluid machine is employed, pulsation of suction fluid may occur due to the displacement of the flow rate introduced into the suction space. When the fluid machine introduces air which externally exists, the suction pulsation may cause noise.

The vacuum pump of Japanese Unexamined Patent Application Publication No. 8-144977 also includes on the vacuum side a roots pump with straight-shaped roots rotors. The flow rate of the suction fluid into the suction space is also displaced in the roots pump with straight rotors, and causes suction pulsation.

When a muffler or a resonator is attached at the suction side, the suction noise may be suppressed. However, the muffler or the resonator is large-sized, and accordingly the whole size of the fluid machine is increased.

The present invention is directed to a composite fluid machine having a first and a second fluid delivering mechanisms, which prevents increase in size while suppressing the suction pulsation.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a composite fluid machine has a first and a second fluid delivering mechanisms. The first fluid delivering mechanism includes an accommodation chamber, a movable body, and a suction space. The movable body is accommodated in the accommodation chamber. The suction space is defined by the accommodation chamber and the movable body. The suction space is connected to the inlet, and the flow rate of the fluid introduced into the suction space is displaced. The movable body performs a suction movement to introduce the fluid into the suction space, and performs a discharge movement to discharge the fluid out from the accommodation chamber. The second fluid delivering mechanism is combined with the first fluid delivering mechanism so as to be located upstream of the first fluid delivering mechanism to deliver the fluid to the suction space of the first fluid delivering mechanism. The second fluid delivering mechanism includes a roots rotor housing and a pair of helical roots rotors,. The helical roots rotors have a respective rotational axis and plural lobes around the rotational axis. The lobes are engaged with each other when the helical roots rotors rotate in the roots rotor housing. The lobes are in a helical shape in such a manner that the lobes are twisted in a respective direction around the rotational axis.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel are set forth with particularity in the appended claims.. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a plane sectional view showing a composite fluid machine having a first and a second fluid delivering mechanisms according to a first embodiment of the present invention;

FIG. 2A is a cross-sectional view taken in line I-I of FIG. 1;

FIG. 2B is a cross-sectional view taken in line II-II of FIG.. 2A;

FIG. 3 is an illustrative view in which helical roots rotors of a helical roots type fluid delivering mechanism as the second fluid delivering mechanism are viewed from the rear side;

FIG. 4A is a side view of one of a pair of helical roots rotors of a helical roots type fluid delivering mechanism as the second fluid delivering mechanism;

FIG. 4B is a side view of the other of the pair of the helical roots rotors;

FIG. 5 is a plan sectional view according to a second embodiment of the present invention;

FIG. 6A is a plan sectional view according to a third embodiment of the present invention; and

FIG. 6B is a cross-sectional view taken in line IV-IV of FIG. 6A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe the first embodiment of a composite fluid machine having a first and a second fluid delivering mechanism of the present invention with reference to FIGS. 1 through 4,. The first fluid delivering mechanism is a positive displacement fluid machine and is embodied as a screw type fluid delivering mechanism.. It is noted that front and rear side of the screw type fluid delivering mechanism are indicated as right-hand side and the left-hand side in FIG. 1.

Referring to FIG. 1, a composite fluid machine 100 includes a screw type fluid delivering mechanism 10 as a first fluid delivering mechanism. The screw type fluid delivering mechanism 10 has a front housing 11. A separation wall 12 is joined to the rear end of the front housing 11. An electric motor M is accommodated in a motor housing M1 and arranged at the rear side of the separation wall 12. The motor housing M1 is connected to the separation wall 12 through a gear housing 13. A housing assembly of the screw type fluid delivering mechanism 10 includes the front housing 11, the separation wall 12, the gear housing 13, and the motor housing M1.

A shaft hole 121 is formed through the separation wall 12. The front housing 11 has an end wall 14, and a shaft hole 141 is formed through the end wall 14. The electric motor M has a rotary shaft 15 so as to extend through the shaft holes 121, 141. The rotary shaft 15 serves as a drive shaft, and is rotatably supported by radial bearings 16, 17 which are accommodated in the shaft holes 121, 141, respectively. Similarly, a shaft hole 122 is formed through the separation wall 12, and a shaft hole 142 is formed through the end wall 14 of the front housing 11. A rotary shaft 18 extends through the shaft holes 122, 142. The rotary shaft 18 serves as a driven shaft, and is rotatably supported by radial bearings 19, 20 which are accommodated in the shaft hole 122 of the separation wall 12 and the shaft hole 142 of the end wall 14. The rotary shafts 15, 18 are arranged parallelly to each other. Shaft seal mechanisms 29, 30 are lip seal type and disposed adjacent to the bearings 16, 19.

The front housing 11 and the partition wall 12 constitute a screw rotor housing 23. The screw rotor housing 23 defines a screw pump chamber 231 as an accommodation chamber for a pair of screw rotors 21, 22. The screw rotor 21 as a movable body is fixed to the rotary shaft 15, and the screw rotor 22 as a movable body is fixed to the rotary shaft 18. The screw rotors 21, 22 are disposed in the screw pump chamber 231 in such a manner the screw rotors 21, 22 engage to each other, forming slight clearance therebetween.

The screw rotor 21 has a screw thread 24, and the width W1 of the screw thread 24 becomes narrower as the screw thread 24 approaches the partition wall 12 from the end wall 14 of the front housing 11. Similarly, the screw rotor 22 has a screw thread 25, and the width W2 of the screw thread 25 becomes narrower as the screw thread 25 approaches the partition wall 12 from the end wall 14 of the front housing 11. The screw pitch p1 of the screw thread 24 of the screw rotor 21 becomes smaller as the screw thread 24 approaches the partition wall 12 from the end wall 14 of the front housing 11. The screw pitch p2 of the screw thread 25 of the screw rotor 22 becomes smaller as the screw thread 25 approaches the partition wall 12 from the end wall 14 of the front housing 11. The front housing 11 has a circumferential wall 28 formed to enclose the screw pump chamber 231, and there is slight clearance between the circumferential wall 28 and the screw threads 24, 25.

As shown in FIG. 2A, the circumferential wall 28 of the front housing 11 has an inlet 281 so as to open therethrough in the vicinity of one axial end of the screw rotor 22, at which the screw pitch p2 is the maximum. The circumferential wall 28 has an outlet 282 so as to open therethrough in the vicinity of the other axial end of the screw rotor 22, at which the screw pitch p2 is the minimum. As shown in FIG. 2B, a suction space H1 is defined in the screw pump chamber 231 by the screw rotors 21, 22. The suction space H1 is connected to the inlet 281 when the fluid is introduced into the screw type fluid delivering mechanism 10. The volume of the fluid introduced into the suction space H1 per unit time is displaced in accordance with the rotation of the screw rotors 21, 22. The screw type fluid delivering mechanism 10 corresponds to the first fluid delivering mechanism in which the flow rate of the fluid introduced into the suction space H1 is displaced.

As shown in FIG. 1, the rotary shaft 18 extends through the partition wall 12 and protrudes into the gear housing 13. Gears 26, 27 are fixed to the rotary shafts 15, 18 respectively in the gear housing 13 in a mutually engaged state. When the electric motor M is operated, the rotary shaft 15 rotates in the direction indicated by an arrow R1 in FIG. 1, and the screw rotor 21 is rotated integrally with the rotary shaft 15 in the direction of the arrow R1. The rotary shaft 18 receives the driving force from the electric motor M through the gears 26, 27. The rotary shaft 18 is rotated in the direction indicated by an arrow R2, which is the counter direction to the rotational direction of the rotary shaft 15. Accordingly, the screw rotor 22 is rotated integrally with the rotary shaft 18 in the direction of the arrow R2.

A helical roots type fluid delivering mechanism 37 as a second fluid delivering mechanism is combined with the screw type fluid delivering mechanism 10. A roots rotor housing 31 of the helical roots type fluid delivering mechanism 37 is joined to the end wall 14 of the front housing 11. The rotary shafts 15, 18 extending through the end wall 14 protrude into the roots rotor housing 31. In the roots rotor housing 31, a pair of helical roots rotors 32, 33 is accommodated. The helical roots rotor 32 is fixed to the rotary shaft 15 and the helical roots rotor 33 is fixed to the rotary shaft 18. The roots rotor housing 31 and the end wall 14 of the front housing 11 define a roots pump chamber 311. The helical roots rotors 32, 33 are disposed in the roots pump chamber 311 in a mutually engaged state having slight clearance therebetween.

The rotary shaft 15 has a rotational axis 151, and the rotary shaft 18 has a rotational axis 181. FIG. 3 illustrates the helical roots rotors 32, 33 as viewed from the rear side in order to explain the twisted states of the helical roots rotors 32, 33. As shown in FIG. 3, the helical roots rotor 32 has three lobes 34 which protrude in the radial direction of the rotary shaft 15. Similarly, the helical roots rotor 33 has three lobes 35 which protrude in the radial direction of the rotary shaft 18. The lobes 34 of the roots rotor 32 are aligned equiangularly at regular intervals of 120 degrees around the rotational axis 151 of the rotary shaft 15 so as to have a rotationally-symmetrical form of 120 degrees. The lobes 35 of the roots rotor 33 are aligned equiangularly at regular intervals of 120 degrees around the rotational axis 181 of the rotary shaft 18 so as to have a rotationally-symmetrical form of 120 degrees.

As shown in FIG. 4A, the lobes 34 are formed in a helical form in such a manner that the roots rotor 32 is twisted helically in a clockwise direction around the axis of the rotor 32, that is, the rotational axis 151 of the rotary shaft 15. As shown similarly in FIG. 4B, the lobes 35 are formed in a helical form in such a manner that the roots rotor 33 is twisted helically in a counterclockwise direction around the axis of the rotor 33, that is, the rotational axis 181 of the rotary shaft 18. In other words, the lobes 34, 35 are formed in a helical form in such a manner that the lobes 34, 35 are twisted helically from end to end around the rotational axes 151, 181 in a respective predetermined direction as the lobes 34, 35 travel in the axial direction or the rotary shaft 15, 18. The lobes 34, 35 have its twist angle Φ, which is defined by angular difference of the lobes 34, 35 at both axial end surfaces. The twist angle of lobes 34, 35 of the roots rotors 32, 33 are 60 degrees end-to-end in the first embodiment,. FIG. 3 illustrates both end surfaces of the twisted roots rotors 32, 33 in the axial direction of the rotational axes 151, 181. The twist angle Φ of the lobes 34, 35 of the helical roots rotors 32, 33 is set so as to satisfy the equation Φ=(360°/2n)X, where n is the number of lobes per roots rotor and X is a positive integer. In the first embodiment, the number of the lobes 34, 35 is three, and the twist angle is 60 degrees.

As shown in FIG. 2A and 3, an inlet 361 and an outlet 362 for the roots pump chamber 311 are formed through a circumferential wall 36 of the roots rotor housing 31 so as to connect the roots pump chamber 311 with the inlet 361 and the outlet 362. A suction space H2 is defined in the roots pump chamber 311 by the helical roots rotors 32, 33 so as to be connected to the inlet 361. The rotary shafts 15, 18, the roots rotor housing 31, and the helical roots rotors 32, 33 constitute the helical roots type fluid delivering mechanism 37,.

The rotary shaft 15 as the drive shaft is connected to the screw rotor 21 as one of the pair of the screw rotors 21, 22 for the screw type fluid delivering mechanism 10. The rotary shaft 15 is also connected to the helical roots rotor 32 as one of the pair of the helical roots rotors 32, 33 for the helical roots type fluid delivering mechanism 37. The rotary shaft 18 as the driven shaft is connected to the screw rotor 22 as the other of the pair of the screw rotors 21, 22 for the screw type fluid delivering mechanism 10. The rotary shaft 18 is also connected to the helical roots rotor 33 as the other of the pair of helical roots rotors 32, 33 for the helical roots type fluid delivering mechanism 37.

The outlet 362 of the helical roots type fluid delivering mechanism 37 and the inlet 281 of the screw type fluid delivering mechanism 10 are connected through an introduction pipe 38. That is, the helical roots type fluid delivering mechanism 37 is located upstream of the screw type fluid delivering mechanism 10. When the electric motor M is operated, the rotary shaft 15 is rotated in the direction of the arrow R1, and the rotary shaft 18 is rotated in the direction of the arrow R2, and the screw rotors 21, 22 and the helical roots rotors 32, 33 are rotated integrally with the rotary shafts 15, 18. As the helical roots rotors 32, 33 are rotated, the air which serves as the fluid in this embodiment, is introduced into the suction space H2, delivered to the outlet 362, and then discharged out from the outlet 362 to the introduction pipe 38.

While the screw rotors 21, 22 rotate, the screw rotors 21, 22 perform suction movement in which the air is introduced into the suction space H1, and perform discharge movement in which the air is discharged out from the screw pump chamber 231. The air in the introduction pipe 38 is introduced into the suction space H1 due to the rotation of the screw rotors 21, 22. The air introduced into the suction space H1 is delivered from the inlet 281 to the outlet 282 while being compressed, and then is discharged out from the screw pump chamber 231.

According to the above first preferred embodiment, the following advantageous effects are obtained.

-   (1) In the screw type fluid delivering mechanism 10, the flow rate     of the fluid introduced into the suction space H1 is displaced,. In     other words, the increased volume of the fluid into the suction     space H1 per unit time is displaced. This displacement causes the     suction pulsation, and transferred to the outlet 362 through the     introduction pipe 38. The suction pulsation, however, does not pass     through the helical roots type fluid delivering mechanism 37 between     the helical roots rotors 32, 33, or between the roots rotor housing     31 and the helical roots rotors 32, 33. In other words, the helical     roots type fluid delivering mechanism 37 cut off the suction     pulsation occurred by the screw type fluid delivering mechanism 10     to the suction side (inlet 361) of the helical roots type fluid     delivering mechanism 37.

The suction space H2 of the helical roots type fluid delivering mechanism 37 is connected to the inlet 361 and is defined by the pair of the helical roots rotors 32, 33 which engage with each other in the roots rotor housing 31. The flow rate of the fluid into the suction space H2 per unit time is not substantially displaced in the helical roots type fluid delivering mechanism 37. When the flow rate of the fluid into the suction space H2 is not displaced, the suction pulsation is extremely small.

Therefore, in the composite fluid machine 100 having the screw type fluid delivering mechanism 10 and the helical roots type fluid delivering mechanism 37 with the helical roots rotors 32, 33, the suction pulsation transferred to the suction side of the helical roots type fluid delivering mechanism 37 is extremely small.

-   (2) The composite fluid machine 100 having the screw type fluid     delivering mechanism 10 and the helical roots type fluid delivering     mechanism 37 according to the first embodiment is downsized,     compared to the case in which a muffler or a resonator with a large     configuration is utilized. -   (3) The screw type fluid delivering mechanism 10 of the composite     fluid machine 100 discharges highly pressurized fluid with high flow     rate in spite of the compact size, and achieves a high efficiency,.     The composite fluid machine 10 having the screw type fluid     delivering mechanism 10 and the helical roots type fluid delivering     mechanism 37 achieves downsizing and high efficiency while     suppressing the suction pulsation. -   (4) The rotary shaft 15 is shared by the screw type fluid delivering     mechanism 10 and the helical roots type fluid delivering mechanism     37. In other words, the rotary shaft 15 serves as the drive shaft of     the screw rotor 21 for the screw type fluid delivering mechanism 10     and as the drive shaft of the helical roots rotor 32 for the helical     roots type fluid delivering mechanism 37. Similarly, the rotary     shaft 18 is shared by the screw type fluid delivering mechanism 10     and the helical roots type fluid delivering mechanism 37. The rotary     shaft 18 serves as the driven shaft of the screw rotor 22 for the     screw type fluid delivering mechanism 10 and as the drive shaft of     the helical roots rotor 33 for the helical roots type fluid     delivering mechanism 37. Such a structure prevents entire     configuration of the composite fluid machine 100 from increasing.

The following will describe a second embodiment of the present invention as embodied in a composite fluid machine in which a scroll type fluid delivering mechanism serves as a first fluid delivering mechanism with reference to FIG. 5. In the following second embodiment, the same reference numerals and symbols as used in the description of the first embodiment are used and the description of the same parts and elements will be omitted or simplified.

A composite fluid machine 200 has a scroll type fluid delivering mechanism 39 as a positive displacement fluid machine which serves as the first fluid delivering mechanism. The scroll type fluid delivering mechanism 39 includes a movable scroll 40, a fixed scroll 44, and an electric motor 41. The movable scroll 40 is accommodated in an accommodation chamber 441 formed in the fixed scroll 44 so as to perform an orbital movement. A suction space H3 is defined by the movable scroll 40 and the fixed scroll 44 at the outer periphery thereof, and is connected to an inlet 43. The electric motor 41 serves as a drive source of the scroll type fluid delivering mechanism 39. The electric motor 41 includes a drive shaft 42 which is connected to the movable scroll 40. When the drive shaft 42 of the electric motor 41 is rotated, the movable scroll 40 as a movable body orbits, and the flow rate of the fluid into the suction space H3 is displaced. The movable scroll 40 and the fixed scroll 44 engage with each other to form a compression chamber 45 therebetween. Due to the orbital movement of the movable scroll 40, the compression chamber 45 is shifted toward the inner periphery of the scroll type fluid delivering mechanism 39 while gradually decreasing its volume and compressing the air introduced through the suction space H3. The orbital movement of the movable scroll 40 corresponds the suction movement in which the air is introduced into the suction space H3, and also corresponds the discharge movement in which the air is discharged from the accommodation chamber 441.

In the composite fluid machine 200, a helical roots type fluid delivering mechanism 37A as the second fluid delivering mechanism is combined to a motor housing 411 of the electric motor 41. The helical roots type fluid delivering mechanism 37A has helical roots rotors 32, 33 in a roots pump chamber 311 defined in a roots rotor housing 31A. The helical roots rotors 32, 33 are fixed to rotary shafts 46, 47, respectively. The rotary shaft 46 is rotatably supported by a partition wall 52 and the roots rotor housing 31A through radial bearings 48, 49. The rotary shaft 47 is rotatably supported by the partition wall 52 and the roots rotor housing 31A through radial bearings 50, 51. The rotary shaft 46 extends through a gear housing 53 and protrudes into the motor housing 411 of the electric motor 41. The drive shaft 42 of the electric motor 41 is connected to the rotary shaft 46.

Gears 26, 27 are accommodated in the gear housing 53. The gear 26 is fixed to the rotary shaft 46 in the gear housing 53. The gear 27 is fixed to the rotary shaft 47 in the gear housing 53 in an engaged state with the gear 26. When the electric motor 41 is operated, the drive shaft 42 and the rotary shaft 46 are rotated in the direction indicated by an arrow R1, and the helical roots rotor 32 is rotated integrally with the drive shaft 42 and the rotary shaft 46 around the rotational axis 461 in the direction of the arrow R1. The rotary shaft 47 receives the drive force from the electric motor 41 through the gears 26, 27. The rotary shaft 47 is rotated in the counter direction to the rotary shaft 46 as indicated by an arrow R2, and the helical roots rotor 33 is rotated integrally with the rotary shaft 47 around the rotational axis 471 in the direction of the arrow R2.

The air is discharged from an outlet 362 of the helical roots type fluid delivering mechanism 37A in accordance with the rotation of the helical roots rotors 32, 33 and is introduced into the suction space H3 through the introduction pipe 38 and the inlet 43 of the scroll type fluid delivering mechanism 39. Then the air is delivered into the compression chamber 45, and is compressed in accordance with the decrease in the volume of the compression chamber 45, and is discharged through a discharge port 54 to a discharge chamber 56, pushing away a discharge valve 55. The suction pulsation occurs in the scroll type fluid delivering mechanism 39 in which the flow rate of the fluid introduced into the suction space H3 is displaced. The helical roots type fluid delivering mechanism 37A, however, cut off the suction pulsation so as not to transfer the suction pulsation to the suction side of the helical roots type fluid delivering mechanism 37A.

The following will describe the third embodiment of a composite fluid machine of the present invention, in which the first fluid delivering mechanism is embodied as a vane type fluid delivering mechanism with reference to FIG. 6. In the third embodiment, the same reference numerals and symbols as used in the description of the above embodiments are used and the description of the same parts and elements will be omitted or simplified.

A composite fluid machine 300 has a vane type fluid delivering mechanism 74 as a positive displacement fluid machine which serves as a first fluid delivering mechanism. As shown in FIG. 6A, a front housing 57 and a rear housing 58 are joined together so as to fixedly dispose a cylinder 59 therein. A hole with an elliptical cross-section is formed through the cylinder 59. The cylinder 59 is sandwiched by a front side plate 60 and a rear side plate 61 so as to close the both opening ends of the cylinder 59 and define a rotor chamber 62 with an elliptical cross-section therein. Shaft holes 63, 64 are formed through the side plates 60, 61 A drive shaft 65 is rotatably supported in the shaft holes 63, 64. A rotor 66 with a circular cross-section is fixed to the drive shaft 65 and accommodated in the rotor chamber 62. As shown In FIG. 6B, plural slots 67 are formed in the rotor 66, and a vane 68 is accommodated in each of the slots 67 in such a manner that the vane 68 is inserted in and retracted from the outer periphery of the rotor 66. The rotor 66 corresponds a movable body accommodated in the rotor chamber 62 as an accommodation chamber.

As shown in FIG. 6A, an oil separation chamber 70 is defined by the rear housing 58 and the rear side plate 61. The oil separation chamber 70 is connected to a discharge chamber 72. The separated lubricating oil is stored at the lower portion of the oil separation chamber 70. The lubricating oil in the oil separation chamber 70 is supplied to the slot 67 by the pressure in the discharge chamber 72. The end of the vane 68 is pressed against the inner circumferential surface of the cylinder 59 due to the pressure of the supplied lubricating oil. As the result, plural compression chambers 69 and a suction space H4 are defined by the adjacent two vanes 68, the outer circumferential surface of the rotor 66, the inner circumferential surface of the cylinder 59, and inner end surfaces of the both side plates 60, 61. The suction space H4 is connected to an inlet 76 through a suction passage 73. The compression chambers 69 are communicated to the discharge chamber 72 through an outlet 71 at a position at a predetermined rotational angle.

The drive shaft 65 and the rotor 66 are rotated integrally. When the rotor 66 is rotated, the air in the suction passage 73 is introduced into the suction space H4, and with further rotation of the rotor 66, two adjacent vanes 68 define a compression chamber 69, and the compression process is performed so as to decrease the volume of the compression chamber 69. The compressed air in the compression chamber 69 is discharged to the discharge chamber 72 by pushing away a discharge valve 75. The rotation of the rotor 66 serves as a suction movement for introducing the air into the suction space H4 and also as a discharge movement for discharging the air from the rotor chamber 62.

The helical roots type fluid delivering mechanism 37A as the second fluid delivering mechanism is combined with the above-constructed vane type fluid delivering mechanism 74. The rotary shaft 46 of the helical roots type fluid delivering mechanism 37A is connected to the drive shaft 65 of the vane type fluid delivering mechanism 74, and the drive shaft 65 and the rotary shaft 46 are rotated integrally. The air discharged from the outlet 362 of the helical roots type fluid delivering mechanism 37A is delivered to the suction passage 73 of the vane type fluid delivering mechanism 74 through the introduction pipe 38.

In the vane type fluid delivering mechanism 74 in which the flow rate of the fluid introduced into the suction space H4 is displaced, the suction pulsation is occurred. The helical roots type fluid delivering mechanism 37A, however, cuts off the suction pulsation so as not to transfer the suction pulsation to the suction side of the helical roots type fluid delivering mechanism 37A.

The present invention is not limited to the above-described embodiments, but may be variously modified within the scope of the invention, as exemplified below.

In the first embodiment, the helical roots type fluid delivering mechanism 37 may be driven by an independent electric motor other than the electric motor M of the screw type fluid delivering mechanism 10. In this case, the helical roots type fluid delivering mechanism 37 may be integrally combined with the screw type fluid delivering mechanism 10, or may be formed so as to have independent shafts and a housing from the screw type fluid delivering mechanism 10.

A straight roots type fluid delivering mechanism with roots rotors which are not twisted may be applied to the present invention instead of the above screw type, scroll type, or vane type fluid delivering mechanisms as a first fluid delivering mechanism,. The flow rate of the fluid introduced into the suction space is displaced in the straight roots type fluid delivering mechanism, and suction pulsation may occur. When the straight roots type fluid delivering mechanism is combined with the helical roots type fluid delivering mechanism of the present invention, the suction pulsation is suppressed.

A piston type fluid delivering mechanism in which a suction space is defined by a piston in a cylinder bore may be applied as a first fluid delivering mechanism to the present invention.

A helical roots type fluid delivering mechanism having helical rotors with more than four lobes, or with two lobes may be applied to the present invention.

A helical roots type fluid delivering mechanism in which the twist angle Φ of the lobes does not satisfy the quotation Φ=(360°/2n)X may be applied to the present invention. When such a helical roots type fluid delivering mechanism is combined at a suction side of a fluid delivering mechanism in which suction pulsation has developed heavily, the suction pulsation is effectively suppressed.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims. 

1. A composite fluid machine having a first and a second fluid delivering mechanisms, the first fluid delivering mechanism comprising: an accommodation chamber; a movable body being accommodated in the accommodation chamber; a suction space defined by the accommodation chamber and the movable body, wherein the suction space is connected to an inlet, wherein the flow rate of the fluid introduced into the suction space is displaced; wherein the movable body performs a suction movement to introduce the fluid into the suction space, and the movable body performs a discharge movement to discharge the fluid out from the accommodation chamber; and the second fluid delivering mechanism which is combined with the first delivering mechanism so as to be located upstream of the first fluid delivering mechanism to deliver the fluid to the suction space of the first fluid delivering mechanism, the second fluid delivering mechanism comprising: a roots rotor housing; a pair of helical roots rotors having a respective rotational axis and plural lobes around the rotational axis, wherein the lobes are engaged with each other when the helical roots rotors rotate in the roots rotor housing, wherein the lobes are in a helical shape in such a manner that the lobes are twisted in a respective direction around the rotational axis
 2. The composite fluid machine according to claim 1, wherein the movable body of the first fluid delivering mechanism is formed by a pair of rotors which engage with each other while rotating in the accommodation chamber to introduce the fluid into the suction space and to discharge the fluid out from the accommodation chamber.
 3. The composite fluid machine according to claim 2, further comprising: a drive shaft being connected to one of the pair of the rotors for the first fluid delivering mechanism, wherein the drive shaft is connected to one of the pair of the helical roots rotors for the second fluid delivering mechanism; and a driven shaft being connected to the other of the pair of the rotors for the first fluid delivering mechanism, wherein the driven shaft is connected to the other of the pair of the helical roots rotors for the second fluid delivering mechanism.
 4. The composite fluid machine according to claim 1, further comprising: a drive shaft being connected to the movable body of the first fluid delivering mechanism, wherein the drive shaft is connected to one of the pair of the helical roots rotors for the second fluid delivering mechanism.
 5. The composite fluid machine according to claim 1, wherein the first fluid delivering mechanism has a pair of screw rotors as the movable body which engage with each other while rotating in the accommodation chamber.
 6. The composite fluid machine according to claim 1, wherein the accommodation chamber of he first fluid delivering mechanism is formed in a fixed scroll, and wherein a movable scroll as the movable body performs an orbital movement in the accommodation chamber while engaging with the fixed scroll.
 7. The composite fluid machine according to claim 1, wherein the first fluid delivering mechanism comprising: a rotor chamber as the accommodation chamber; a rotor as the movable body being accommodated in the rotor chamber, wherein the rotor has plural slots; and plural vanes being inserted in the slots; wherein the vanes, the rotor defines the suction space in the rotor chamber.
 8. The composite fluid machine according to claim 1, wherein the lobes of the second fluid delivering mechanism have a twist angle Φ which is set so as to satisfy the following equation.: Φ=(360°/2n)X, where n is the number of the lobes and X is a positive integer.
 9. The composite fluid machine according to claim 1, wherein the first fluid delivering mechanism compresses the fluid in the accommodation chamber. 